OTTAWA -- Canadian adults have a so-so record of physical activity, says a global couch potato survey. But it’s our kids who urgently need to ditch their iPhones and run somewhere.

Younger teens in this country are two to three times as inactive as adults, says a survey by The Lancet, one of the world’s most influential medical journals.

It finds our level of physical activity ranks high among Western nations -- better than in the U.S., and better than those pesky Swedes who were supposed to be fitter at age 60 than Canadians at 30.

But it appears to be a myth that healthy, active teenagers are later turning into sedentary adults.

The Lancet says between 70 and 79 per cent of Canadian boys aged 13 to 15 are inactive, and so are 80 to 89 per cent of girls the same age.

(The findings for teens are shown in graph form, with increments of 10 percentage points.)

There’s less time in school for physical education, and Canadian and U.S. students are increasingly riding to school in a bus or their parents’ car, the study says.

“Reductions in physical activity have been recorded . . . in Canadian boys and girls aged 8-16 years from 2001 to 2006,” it says.

All stats are based on self-reporting.

In Canada, 33.9 per cent of adults are inactive, it says, against a global figure of 31.1 per cent.

As with most countries, men fare a little better. The study says 32.3 per cent of men and 35.4 per cent of women are inactive.

The difference between teens and adults comes partly from the stricter definition of exercise for teenagers.

The Lancet wants adults to do at least five half-hour periods of moderate activity per week, or three 20-minute bursts of a vigorous workout.

But it says teens aged 13 to 15 should get 60 minutes a day of exercise to build a healthy body.

“The human body has evolved in such a way that most of its systems (skeletal, muscle, metabolic and cardiovascular) do not develop and function in an optimum way” unless they are physically active.

We’ve known for years about the dangers of inactivity in a world of labour-saving machines. What’s new is the ability to measure rates of inactivity globally, and compare countries, regions and age groups.

For instance, that inactivity rate of Canadian adults (33.9 per cent) is better than the rate in the U.S. (40.5 per cent), Sweden (44.2 per cent) or Denmark (35.1 per cent).

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